Trapped air within a sprinkler system refers to pockets of compressed gas lodged in the pipes, often following repairs, winterization, or a temporary interruption in the water supply. These air pockets disrupt the normal hydraulic balance, leading to inconsistent water delivery and pressure fluctuations. Removing this trapped air, known as bleeding the system, is necessary for maintaining consistent water coverage across the landscape. Proper bleeding ensures all components receive water at the correct pressure and guarantees accurate spray patterns from the sprinkler heads.
Identifying Trapped Air and Pre-Bleed Preparation
The presence of air in the irrigation lines usually presents several noticeable symptoms during operation. A common sign is a sputtering or misty output from the sprinkler heads instead of a solid stream, indicating that air is being expelled along with the water. You may also observe erratic spray patterns or zones that fail to activate entirely because the air pocket prevents the necessary pressure from building up. A particularly damaging symptom is a loud banging or gurgling noise, known as water hammer, which occurs when water violently compresses a trapped air pocket, potentially damaging pipes and fittings.
Before beginning the bleeding procedure, perform a few preparatory steps to ensure safety and efficiency. Locate the main shut-off valve for the irrigation system, typically found near the water meter or the backflow prevention device. Turn this valve completely off to stop the flow of water and depressurize the main line. This prevents uncontrolled water flow when opening downstream valves. Gather simple tools, such as a flathead screwdriver or the specific wrench for your backflow device, along with rags to manage small water leaks.
Bleeding Air from the Main Supply and Backflow Preventer
The first stage of air removal involves the primary components that feed the entire system, particularly the main supply line and the backflow prevention device. The backflow preventer often contains test cocks or bleed valves useful for this process. With the main water supply still off, slowly open the downstream test cock, which is located closest to the sprinkler zones. This releases any residual pressure trapped within the assembly.
Once the initial pressure is released, slowly reopen the main water supply valve to allow water back into the system. Turn this valve gradually to minimize the risk of water hammer. As the system repressurizes, return to the backflow device and slowly open the test cocks, starting with the one furthest from the water source. Allow the air to escape; you will typically hear a distinct hissing sound followed by a turbulent mixture of air and water. Keep the cock open until a steady, air-free stream of water emerges, then close it securely, repeating this process for the other test cocks on the device.
Removing Air Using Individual Zone Valves
After clearing the main supply lines, the next step is to address any air that remains trapped in the lateral lines that feed each specific zone. This is done at the manifold or valve box, where the zone control valves are located. One effective method is the manual bleed, which involves using the bleed screw or lever found on the exterior of the zone valve. Slowly turn the manual bleed screw—or rotate the solenoid cap a quarter-turn counter-clockwise—until you hear water rushing into the zone line.
Allow the water to flow for approximately 30 to 60 seconds, or until you observe a steady, smooth flow coming out of the sprinkler heads in that specific zone. The water flow forces the air remaining in the lateral piping to escape through the heads, confirming the line is clear. Once the water runs smoothly without sputtering or hissing, fully close the bleed screw or tighten the solenoid cap to shut the valve. This method works well for purging localized air pockets.
An alternative approach is to use the system’s controller to activate each zone sequentially. With the main water supply fully on, program the controller to run the first zone for two to three minutes. The pressure from the main line will push the trapped air through the zone’s pipes and out the sprinkler heads. Observe the heads for a smooth, consistent spray pattern. Once the spray pattern stabilizes, move on to the next zone and repeat the process, then reset the system controller to its regular watering schedule.